Process for chemically depositing nickel on a synthetic resin base material

ABSTRACT

A PROCESS FOR THE CHEMICAL DEPOSITION OF NICKEL ON A SYNTHETIC RESIN BASE MATERIAL, CHARACTERIZED BY ETCHING THE RESIN BASE MATERIAL IN A NEW ETCHING SOLUTION CONTAINING A PALLADIUM COMPOUND AS THE ADDITIVE THEREBY ELIMINATING THE CONVENTIONAL SENSITIZING AND ACTIVATING TREATMENTS, AND CHEMICALLY DEPOSITING NICKEL ON THE ETCHED RESIN BASE MATERIAL FROM A NEW CHEMICAL NICKEL PLATING BATH CONTAINING AS THE ADDITIVES A WATER-SOLUBLE LEAD COMPOUND AND A SECOND REDUCING COMPOUND SUCH AS ASCORBIC ACID, THEREBY OBTAINING THE NEW PLATING BATH HAVING A BETTER PLATING CAPABILITY AND LONGER LIFETIME.

United States Patent 3,672,940 PROCESS FOR CHEMICALLY DEPOSITING NICKEL ON A SYNTHETIC RESIN BASE MATERIAL Kiyotaka Funada, Chigasaki, Takashi Shinohara, Yokohama, and Hiroko Imai, Tokyo, Japan, assignors to Nihon Kagaku Kizai Kabushiki Kaisha, Tokyo, Japan No Drawing. Filed Aug. 3, 1970, Ser. No. 60,628 Claims priority, application Japan, Aug. 8, 1969,

44/62,687 Int. Cl. B44d 1/092; C23c 3/02 US. Cl. 117-47 A 7 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a process for forming a nickel coating on a synthetic resin base material.

A process for coating a synthetic resin base material with nickel has greatly been improved and consequently the adhesion of a nickel coating to a resinous material has been improved. Thus, such nickel coated synthetic resin articles have been in great demand instead of die-cast zinc and aluminum articles for the same use in many industrial fields.

However, since the electroplating of a synthetic resin article according to such a conventional process requires not a few preliminary steps of rendering the resinous article electrically conductive, it will cost a lot of money for industrial equipments if industrialized and will need operators of long-period experience to be carried out satisfactorily. Thus there is a tendency that even operators skilled in the art produce coated articles where the coating is not securely attached to the base article and is not uniformly formed thereon. In addition to these disadvantages, the conventional process will produce nickel coatings which have clouding with non-uniform thickness.

A conventional process for forming chemical copper or nickel coatings, which is now prevalently in use usually as the preliminary one for the subsequent electroplating, typically comprises as many as 16 steps shown hereunder:

I Degreasing I -r I Washing with water I Etching I -v IWashing with water Washing with water Washing with water -1 I sensitizing I I Washing with water I Washing with water I Activating I I Washing with water I Chemical coating I Washing with water I Washing with water I 3,672,940 Patented June 27, 1972 The chemical coating thus washed with water is usually followed by electroplating to increase the coating in thickness.

In the practice of said conventional, chemical coating, a synthetic resin base material is first degreased with a weakly alkaline solution, washed with water and immersed in an etching solution consisting of chromic acid and sulfuric acid to provide the base material with receptivity for a metal coating to be formed thereon. In this treatment the composition and temperature of the etching bath as well as the time of immersion therein should properly be controlled to obtain a satisfactory etching. 'If the etched basematerial is immersed in the subsequent sensitizing bath containing stannous ion without thoroughly removing the chromium ion adsorbed on the surface thereof during the etching treatment, the still remaining chromium ion will hinder the stannous ion from being adsorbed on the base material from the sensitizing bath and will oxidize the stannous ion present in the sensitizing bath thereby accelerating the using up of this bath. Thus, the etched base material should be washed with water usually three times to remove the chromium ion therefrom before immersed in the subsequent sensitizing bath.

The sensitizing bath usually consists of a dilute solution of stannous chloride in hydrochloric acid and should be such that the stannous ion therefrom is allowed to be adsorbed on the sensitized base material in an amount necessary and sufiicient to reduce palladium ion to be attached to the base material in the following activating step. An insufficient amount of the stannous ion adsorbed will be a cause for forming a skip plating, and the introduction of excessive stannous ion into the activating bath will reduce unnecessarily too much of the palladium ion present therein thereby promoting the degradation of this bath. And further, if the activated base material is carried into a chemical plating bath together with the unnecessarily reduced, minutely particulate metallic palladium attached thereto, a nickel coating with a rough surface will be formed on the base material.

As the activating bath, a bath consisting of a dilute solution of palladium chloride in hydrochloric acid will commonly be used when a chemical nickel coating is to be obtained. The stannous ion adsorbed on the base material from the sensitizing bath, when the base material is immersed in the activating bath containing palladium ion, will reduce the palladium ion to metallic palladium in fine particulate form which is then securely adsorbed on the base material. A chemical nickel skip plating will be formed if the amount of metallic palladium adsorbed is insufiicient, while undesirable palladium ion, if carried into a chemical nickel plating bath with the base material, will function as catalytic nuclei thereby depositing and suspending nickel in the bath or, in some cases, decomposing the bath with the result that it cannot be used any further.

There have hitherto been proposed various processes for the formation of a chemical nickel coating, in which processes some of the above-mentioned conventional troublesome steps are eliminated. However, many of these processes have their own disadvantages and they are therefore not considered to be practicable.

This invention relates to a process for forming a chemical nickel coating on a synthetic resin base material, characterized in that it uses both a new etching bath prepared by adding a very small amount of palladium ion to a conventional etching bath containing a mixed solution of sulfuric and chromic acids and a new plating bath prepared by adding a second reducing agent and an anti-decomposition agent for the plating bath toa conventional chemical nickel plating bath containing nickel and hypophosphite ions, whereby the etching and activating treatments can be carried out at a time by use of the new etching bath and the sensitizing treatment can be dispensed with. Thus the process of this invention may comprise much fewer steps than the conventional ones and it usually comprises only 9 steps as shown below:

Degreasing iwashing with water I Etchingandactivating i Washing with water The synthetic resin base material treated by the process i of this invention is then subjected to electroplating.

Chemical nickel plating baths which may be used in the practice of this invention, are prepared by adding ascorbic acid or a salt thereof as a second reducing agent and a water-soluble lead compound as an anti-decomposition agent for the bath to a conventional acidic or alkaline bath containing nickel and hypophosphite ions together with an organic acid, boron compound and other suitable compounds as a complexing and/ or buffer agent.

When palladium ion is introduced in such a chemical plating bath containing nickel and hypophosphite ions, the hypophosphite ion will, with aid of the catalytic action of metallic palladium, cause the following reaction:

The hydrogen atoms thus produced are adsorbed on the surface of the catalytic metal to activate the surface thereby reducing the nickel ion and depositing metallic nickel as indicated below:

The metallic nickel thus deposited then functions as a catalyst in the reaction (1) thereby allowing the reaction to proceed while forming a nickel coating. Thus, in order to plate with nickel a metal which is catalytically inactive in the reaction (1), the nickel is necessary to deposit on the inactive metal by means of substitution reaction or galvanization.

Such galvanization is not applicable to a synthetic resin material which is a poor electric conductor. Thus it is necessary to subject the resin material to the activating treatment in order to adsorb a catalytic material, such as metallic palladium, thereon for the subsequent deposition of nickel with aid of the catalyst as crystallizing nuclei. If the metallic palladium adsorbed on the resin material in the activating treatment is peeled off the resin material when immersed in the plating bath or if the resin material is immersed in the plating bath together with some of the activating solution of palladium still remaining on the resin material because of insuflicient washing thereof with water and the solution is dispersed throughout the plating bath, the palladium thus introduced will vform catalytic nuclei thereby causing such reactions as above and depositing nickel as a precipitate in the plating bath. If such nickel deposited is attached to the resin material, it will form a spotted nickel coating thereon. In addition, if the plating bath is incorporated with too much of the palladium, it will continue to deposit nickel until depletion of the nickel ion therein and it may entirely decompose. If, for too much fear of this, the resin material from the activating bath is too much repeatedly washed with water, some portions of the surface thereof will not be covered with nickel when immersed in the nickel p1at- 4 ing bath because the palladium once adsorbed on said portions may have been washed away by said too much washing. The foregoing is the reason why even workmen very skilled in the art cannot necessarily produce satisfactorily nickel-coated articles only.

It is considered that, in the chemical nickel plating bath according to this invention, the ascorbic acid selectively reduces the palladium ion adsorbed on the resinous base material from the etching and activating bath prior to the start of reduction of the nickel ion by the hypophosphite ion thereby preventing the palladium ion from difiusing throughout the plating bath, while the palladium ion dragged into the plating bath together with the resinous base material is occluded or caught in the lead ion, which is a negative catalyst for the reducing action of the hypophosphite ion, thereby losing its catalytic capability. The ascorbic acid may be substituted by its salt and may be used in any desired amounts.

In the plating bath according to this invention, the lead ion should preferably be contained in amounts of not more than 10 p.p.m. since the hypophosphite ion will decrease in reducing power or reducibility if too much of lead ion is present. The plating bath may be acidic or alkaline. It should preferably be at a pH value of 3 to 10 and it will decrease the rate at which nickelis deposited therefrom, when kept at a pH value of not more than 3. The optimum temperature of the plating bath when in use does not have to be changed due to the presence of ascorbic acid in the bath. The .bath may thus be kept at the same suitable temperature as the conventionally used baths, when in use.

Typical etching solutions which may be used in the practice of this invention, comprise. 100-900 cc./l. of conc. H 0-200 cc./l. of phosphoric acid, 900- cc./l. of water, 5-300 g./l. (calculated as CrO of chromic acid anhydride and 005-5 g./l. (calculated as Pd) of a palladium salt and, preferably, 400-900 cc./l. of conc. H 50 0-100 cc./l. of phosphoric acid, 600-100 cc./l. of water, 5-30 g./l. (calculated at Cr0 of chromic acid anhydride and 0.2-5 g./l. (calculated as Pd) of a palladium salt. The chromic acid anhydride may be substituted by potassium dichromate, and the palladium salt is selected from palladium chloride, palladium sulphate and sodium palladium chloride.

Typical nickel plating baths which may be used, comprise 1-18 g./l. (calculated as Ni ion) of a nickel salt, 3-40 g./l. (calculated as hypophosphite ion) of a hypophosphite, 5-100 g./l. of an organic acid, 1-50 g./l. (calculated as ascorbic acid) of an ascorbic acid type compound and l-10 mg./l. (calculated as lead ion) of a lead salt and, preferably, 2-8 g./l. (calculated as Ni ion) of a nickel salt, 5-18 g./l. (calculated as hypophosphite ion) of a hypophosphite, 10-30 g./l. of an organic acid, 10-30 g./l. (calculated as ascorbic acid) of an asconbic acid type compound and 2-7 mg./l. of a lead salt. The baths should be at a pH value of 3-10', preferably, 4-9. The nickel salt may be nickel sulphate, nickel chloride or the like; the hypophosphite is typically sodium hypophosphite; the ascorbic acid type compound may be ascorbic acid, sodium ascorbate or the like; and the organic acid is selected from short chain monocarboxylic acids such as acetic, propionic and butyric acids, and the salts thereof; dicarboxylic acids such as malonic, succinic and adipic acids, and the salts thereof; tricarboxylic acids such as citric acid, and the salts thereof; hydroxycarboxylic acids such as glycolic, lactic, malic and tartaric acids, and the salts thereof; and aminocarboxylic acids such as aminoacetic and aminopropionic acids, and the salts thereof. The salts of these various acids are typically the sodium, potassium, ammonium and other like salts. The lead salt is selected from lead nitrate and acetate. Together with the above-mentioned organic acids, there may be used ammonium chloride, borax and the like.

This invention will be better understood by the following examples.

'EXAMPLE 1 Test pieces (65 mm. x 40 mm. x 3 mm.) of acrylonitrile-butadiene-styrol (ABS) resin (Plating Grade, this resin being the one made by Ube Cycon Co., Ltd., Japan) were degreased with an alkali, washed with water and immersed in an etching solution at 60 C. for 15 minutes to etch them, the etching solution having the following composition:

Concentrated H 80 cc./l 500 Water cc./l 500 Chromic acid anhydride g./ 1-- 15 Palladium chloride g./l 0.5

Some of the thus-etched test pieces, after washed with water, were then immersed in 200 cc. of a novel chemical plating bath at 40 C. for 5 minutes in an attempt to form a nickel coating thereon, the novel plating bath having the following composition:

Nickel sulphate I, g /l 20 'Sodium hypophosphite g./l 15 Adipic acid 2 /l L-ascorbic acid g./l 10 Lead nitrate mg /l 5.5 pH (adjusted with NaOH) 6.0

For comparison, the rest of the etched test pieces, after washed with water, were then immersed in 200 cc. of a conventional chemical plating bath at the same temperature for the same time as above in an attempt to form a nickel coating thereon, the conventional bath having the following composition:

Nickel sulphate g./l 20 Sodium hypophosphite g./l Adipic acid 'g./l 10 L-ascorbic acid Lead nitrate pH (adjusted with NaOH) 6.0

colored precipitates.

EXAMPLE 2 The procedure of Example 1 was repeated, but using the following etching solution and conventional and novel baths under the following operational conditions:

Etching solution:

Concentrated H 80 cc./l 800 Water cc./l 200 Chromic acid anhydride g./l 10 Palladium sulphate g./l 0.5 Temp. of the solution C 40 Time of immersion min 5 CHEMICAL NICKEL PLATING BATHS Conventional Novel bath bath Nickel snl hate g./l 16 16 Sodium hy pohosphlte, g n n Citric acid, g./l 6 2 6 Borax, g./l 2.5 .5 L-ascorbic acid, g./i None 3 Lead acetate, mg./1 None 7 pH of the bath (adjusted with NaOH 8. 0 8.0 Temp. of the bath, 3g 3% Time of immersion, min

The test pieces from the novel bath had a uniform nickel coating formed all over the initial etched surface thereof while the bath was kept transparent during the time of immersion of the test pieces therein; and, on the other hand, the test pieces from the conventional bath had a surface which was dotted with nickel from the bath while the bath remained limpid during the time of immersion of the test pieces.

EXAMPLE 3 The procedure of Example 1 was followed, but using the following etching solution and novel and conventional baths under the following operational conditions:

Etching solution:

Concentrated H 50 cc./ 1-- 500 Water cc./l.. 500 Potassium dichromate g./l 10 Sodium palladium chloride g./l 1 Temp. of the solution C 60 Time of immersion min 10 CHEMICAL NICKEL PLATING BATHS Conventional Novel Nickel sulfate, g./1 20 20 Sodium hypophosphite, g./l 15 15 Sodium, succinate g.ll 15 15 L-ascorbic acid, g./i None 30 Lead acetate, mg./l None 10 pH of the bath (adjusted with NaOH) 4. 0 4.0 Temp. of the bath, C 60 60 Time of immersion, min 3 3 using the following etching solution and conventional and novel baths under the following operational conditions:

Etching solution:

Concentrated H cc./l 860 Phosphoric acid cc./l 50 Water cc./l Potassium dichromate -g./l l7 Palladium sulphate g./l 9 Temp. of the solution C 25 Time of immersion min 5 CHEMICAL NICKEL PLATING BATHS Conventional Novel Nickel chloride, g./l 20 20 Sodium hypophosphite, g 27 27 Sodium succinate, g./l 16 16 L-ascorbic acid, g./1 None 10 Lead acetate, in ./i None 5. 5 pH of the bath (adjusted with N aOH 4. 8 4. 8 Temp. of the path, C 65 65 Time of immersion, min 5 5 The results obtained were as follows:

The novel bath deposited nickel on the etched test pieces to form a uniform nickel coating on the entire surface thereof, during which the bath was maintained transparent. In contrast with this, the conventional bath deposited nickel on the etched test pieces so that the surface thereof was dotted with the nickel thus deposited, during which the bath was kept transparent.

EXAMPLE 5 The procedure of Example 1 was repeated, but using test pieces of polyester (sold under the trademark Lumilar by Toray Inc., Japan), the following etching solution and novel and conventional baths under the following operational conditions:

Etching operation:

Conc. H 80 cc./l 800 Water cc./l 200 Chromic acid anhydride g./l 10 Palladium sulfate g./l 0.5 Temp. of the solution C 60 Time of immersion min 20 CHEMICAL NICKEL PLATING BATHS Conventional Novel bath bath Nickel chloride, g./l 6O 60 Sodium hypo hosphite, g./l 20 20 Citric acid, g. l 100 100 Ammonium chloride, 50 50 Ascorbic acid, g./l None 10 Lead nitrate, mg./ None 7 pFH (adjusted by NaOH). 9 9 emp. of .the bath, C--- 50 50 Time of immersion, min 5 Etching solution:

Cone. H 80 cc./l 500 Water cc./l 500 Chromi e acid anhydride g./l.. 15 Sodium palladium chloride g./l 1 Temp. of the solution C 80 Time of immersion min. 30

CHEMICAL NICKEL PLATING BATHS 8 EXAMPLE 7 Etching solution:

Concentrated H 80 cc./l 500 Water cc l 500 Chromic acid anhydride g./l.. 15 Palladium chloride g./l 0.5 Temp. of the solution C Time of immersion min 15 CHEMICAL NICKEL PLATING BATHS Conventional Novel (Bath A (Bath Dr) S d h h hit ll %2 :2

o rum ypo 05 e, Adipic acid, 511... 15 15 Sodium L-ascorbate, g./l 10 Lead acetate, mg./l 3.7 g H (Adjusted by NaOH) 6 6 emp. of the bath, C 60 60 Time of immersion, min 5 5 The results obtained were that the novel bath deposited nickel on the test pieces thereby forming a uniform nickel coating over the entire surface thereof while keeping the bath transparent, whereas the conventional bath deposited no nickel while forming a dark-colored precipitate.

Experiment 1 For comparison a test was made by repeating the procedure of Example 7, but using a conventional bath A a novel bath D a bath B prepared by adding 10 g./l. of sodium L-ascorbate to a bathA a bath 0; prepared by adding 3.7 mg./l. of lead acetate to a bath A respectively. In the coating step, after the etching step, of the test, test pieces to be coated were treated in such a manner that one test piece was immersed in 200 cc. of the bath for a predetermined period of time (5 min. in this case) before another was in turn immersed under the same conditions as above, in order gpggfi; g g i 45 to investigate the state of a nickel coating formed on ml the test pieces and the change in appearance of the bath. 3g 28 A set of the twenty test pieces P -P mm. x 40 1o 10 mm. x 3 mm.) of ABS resin were prepared for use in time each of the baths.

g 5 50 The experiment showed that a satisfactory result was 50 2 obtained only with the novel bath D The detailed re- 5 sults are shown in the following Table 1.

TABLE 1 Baths used Bath A1 Bath B1 Baths 0; Bath D1 State of coating State of Change in formed and change State of Change in State of Change in coating appearance coating appearance of in appearance of formed, bath formed, formed, formed, of bath bath percent percent percen percent 0 Deeomposed 100 None.

100 Do. 100 Do. 100 Do. 100 Do. 100 D0. 100 Do.

Nora-0%: Test pieces were coated with no or very little nickel; 20%, 50% and 80%: Test pieces were coated with nickel on approximately 20%, 50% and 80% of the surface, respectively. 100%: Test pieces were coated with nickel uniformly on the entire surface.

The test pieces from the novel bath had a nickel Table 1 indicates the following:

coating formed all over the surface thereof and the bath (1) In case of the bath A1:

remained limpid during the test, while those from the conventional bath had a nickel coating formed on about half the surface thereof and the bath formed a darkcolored precipitate.

P to P (pieces Nos. 1 to 4) were coated with no or very little nickel. The bath decomposed while P was immersed therein, thereby making it impossible to continue the test any further.

(2) In case of the bath B P was hardly coated with nickel while the bath decomposed, thereby making it impossible to continue the test any further.

(3) In case of the bath C P and P were hardly coated with nickel, P to P were coated with nickel on 20%, 80% and 50% of the surface, respectively, and P P were coated with nickel on Experiment 2 For comparison, the same procedure as in Example 8 was repeated, but using a bath A a bath B prepared by adding 7 g./l. of sodium L-ascorbate to a bath A a bath C prepared by adding 7 mg./l. of lead nitrate to a bath A and a bath D respectively. In this comparison test, 200 cc. of each of the baths were used and a set of the twenty test pieces (P' to P' were prepared for use in each of the baths.

%, on the average, of the surface, respectively. The 10 The results obtained are shown in Table 2.

TABLE 2 Baths used A2 2 C2 D2 Coating Coating Coating Coating State of coating formed and formed, Change of formed, Change of formed, Change of formed, Change change in appearance of bath percent bath percent bath percent bath percent of bath Test pieces used:

1 0 None 0 Decomposed 100 None. P 0 ..d 100 Do. P' 0 do. 100 Do. P 0 .d0 0 ...do 100 Do. P' -P 0) Not tested Not tested 100 Do.

l Not tested.

bath decomposed while P was immersed, thereby making the test impossible to be continued any further.

entire surface, and the bath did not show any change in appearance throughout the test.

EXAMPLE 8 The procedure of Example 1 was followed, but using the following etching solution and conventional and novel baths under the following operational conditions:

Etching solution:

Concentrated H 80 cc./l- 800 Water cc./l 200 Chromic acid anhydride g./l l0 Palladium sulfate g./l.. 0.5 Temp. of the solution C 50 Time of immersion min 10 CHEMICAL NICKEL PLATING BATHS Conventional Novel (Bath A2) (Bath D2) Nickel sulfate, g./l 16 16 Sodium hypophosphite, g./l 11 11 Citric acid, g./l 10 10 orax, g./l 6 6 Sodium L-aseorbate, 0 7 Lead nitrate, mg. 0 7 pH (adiusted by NaOH) 9 9 Temp. of the bath, C 40 40 Time of immersion, min 3 3 The results obtained showed that the conventional bath deposited no nickel on the etched pieces without change in appearance of the bath (transparent), while the novel bath deposited nickel on the etched test pieces uniformly on the entire surfaces without change in appearance of the bath (transparent).

EXAMPLE 9 The procedure of Example 1 was followed, but using the following etching solution and conventional and novel baths under the following operational conditions:

Etching solution:

Conc. H cc./l 500 Water cc./l 500 Potassium dichromate g./l 10 Sodium palladium chloride (Na PdCl g./l 1 Temp. of the solution C 60 Time of immersion min 10 CHEMICAL NICKEL PLATING BATHS Conventional Novel (Bath A3) (Bath D3) Nickel sulfate, g./l 20 20 Sodium hypophosphit g./l 15 15 Sodium succinate, g./1- 15 15 Sodium L-ascorbate, g./l 0 30 Lead acetate, mg./l 0 5 pH (adjusted by H2SO4) 4 4 Temp. of the bath, C 60 60 Time of immersion, min 3 3 The results obtained were that the conventional bath hardly deposited any nickel on the etched test pieces with a dark-colored precipitate formed therein, whereas the novel one deposited nickel uniformly on the surface of the etched test pieces while keeping the bath transparent.

Experiment 3 A comparative test was made in the same manner as in Example 9, but using each of a conventional bath A a bath B prepared by adding 30 g./l. of sodium L- ascorbate to a bath A and a novel bath D In this experiment 200 cc. of each of the baths were used and a set of the test pieces (P" -P" were prepared for use in each of the baths, as in the other experiments. The results obtained are indicated in Table 3.

. 12 nickel uniformly on the entire surface of each of the test pieces used while it remained limpid.

TABLE 3 Bath used A3 B3 C3 D3 Coating Coating Coating Coating State of coating formed and formed, formed, formed, Change formed, Change change in appearance of bath percent Change of bath percent Change of bath percent of bath percent of bath Test pieces used:

P"; 20 None 100 None None--. 100 None.

P"; Decomposed Decomposed 0 do.. 100 Do.

P"; 0 .do 100 Do.

P"; 0 -do 100 Do.

P" Pm .do 100 Do.

EXPERIMENT 4 For comparison, the procedure of Example 10 was repeated, but using a bath A a bath B prepared by adding 10 g./l. of sodium L-ascorbate to a bath A a bath C prepared by adding 5.5 mg./l. of lead acetate to a bath A and a bath D respectivey. In this experiment, 200 cc. of each of the baths were used and twenty test pieces prepared for each of the baths, as in the previously-mentioned experiments.

The results obtained are indicated in the following table.

TABLE 4 Bath used A4 B4 C4 D4 Coating Coating Coating Coating State of coating formed and iorme formed, formed, Change formed, Change change in appearance of bath... percent Change of bath percent Change of bath percent of bath percent of bath Test pieces used:

' 100 Non 50 None. 100 None.

100 do 50 100 Do. Decompos 50 ...do 100 Do. 50 -..do 100 Do. P -P 50 d 100 Do.

The bath D deposited nickel uniformly on the entire surface of each of P" to P" while it was quite limpid.

EXAMPLE 10 Test pieces used: Styrol resin plaques 45 mm. x 40 mm. x 1.5 mm.

Etching solution:

Conc. H 80 cc./1 860 Phosphoric acid cc./l 50 Water cc./l 90 Potassium dichromate g./ 1-- 17 Palladium sulfate g./l 9 Temp. of the solution C 25 Time of immersion min 5 CHEMICAL'NICKEL PLATING BATHS Conventional Novel (Bath A4) (Bath D4) Nickel chloride, g./l 20 20 Sodium hypophospliite, 27 27 Sodium succinate, g./i- 16 16 Sodium L-ascorbate, g./l 0 10 Lead acetate, mgJl 0 5. 5 pH (adjusted by H2804) 4. 8 4.8 Temp. of the bath, C- 65 65 Time of immersion, min 5 5 The results obtained are as follows:

The conventional bath deposited nickel on the entire surface of only some test pieces used at the early stage of the plating operation, while the bath formed a darkcolored precipitate shortly after the start of the plating operation. On the other hand, the novel bath deposited As seen from Table 4, the results obtained tend to be similar to those obtained in each of the Experiments 1 and 3.

More particularly, the bath A deposited nickel on the entire surface of each of the first to third etched test pieces (P"' to P"' and it decomposed with a darkcolored precipitate being formed when the fourth piece (P was immersed therein. 4

The bath B deposited nickel on the entire surface of the first and second pieces (P' and P' and it decomposed when the third piece (P"';,) was immersed.

The bath 0; deposited nickel on approximately 50% of the surface area of each of all the pieces (P"; to P2 "'20) while it remained limpid.

In contrast with these baths, the bath D according to the present invention deposited nickel uniformly on the entire surface of each of all the pieces (P"' to P while it remained quite limpid without any indication of its decomposition.

What we claim is:

1. A process for chemically depositing nickel on a synthetic resin base material comprising etching the synthetic resin base material in an aqueous etching solution comprising 0.055 g./l., calculated as palladium, of a palladium salt in addition to 900 cc./l. of concentrated sulfuric acid, 0-200 cc./l. of phosphoric acid, 900-100 cc./l. of water and 5-300 g./l. of chromic acid anhydride, and, without otherwise sensitizing and activating, chemically depositing nickel on the etched resin base material from a plating bath comprising 1-10 mg./l., calculated as lead ion, of the water-soluble lead compound selected from the group consisting of lead nitrate and lead acetate and 1-50 g./l., calculated as ascorbic acid, of a second reducing compound selected from ascorbic acid and its salts, in addition to 1-18 g./l., calculated as nickel ion,

of a nickel salt, 3-40 g./l., calculated as hypophosphite ion, of a hypophosphite and 510() g./l. of another organic acid.

2. A process according to claim 1 wherein the palladium salt is selected from the group consisting of palladium chloride, palladium sulfate and sodium palladium chloride.

3. A process according to claim 1 wherein the nickel salt is selected from the group consisting of nickel sulphate and nickel chloride, the hypophosphite is sodium hypophosphite and said organic acid is selected from the group consisting of short-chain mono-, diand tricarboxylic acids, hydroxycarboxylic acids, and aminocarboxylic acids.

4. A process according to caim 1 wherein said palladium salt is present in said aqueous etching solution in an amount of from 0.2-5 g./l., calculated as palladium.

5. A process according to claim 1 wherein said plating bath contains to 30 g./l., calculated as ascorbic acid,

UNITED STATES PATENTS 3,597,267 8/1971 Mallory et al. 3,437,507 4/1969 Jensen 106-1 X 3,459,563 8/1969 Terashima et al. 1061 3,488,166 1/1970 Kovac et al. 117-47 X 3,553,085 1/1971 Heymann 11747 X ALFRED L. LEAVI'IT, Primary Examiner J. A. BELL, Assistant Examiner US. Cl. X.R. 

